1. Field of the Invention
The present invention generally relates to a diffuser plate and a backlight module using the diffuser plate; particularly, the present invention relates to a backlight module for use in a liquid crystal display (LCD) device and a diffuser plate for use in the backlight module.
2. Description of the Prior Art
Backlight modules are widely used in liquid crystal display (LCD) devices, computer keyboards, buttons of cellular phones, advertising billboards, and any other devices that require a light source. In the recent years especially, the markets for flat panel displays are rapidly expanding. As a result, the need for LCD panels in the markets is largely increased at the same time. Furthermore, the functional and structural designs of the backlight modules used in the LCD panels have been diversified, in order to accommodate the emerging market demands for the LCD panels.
However, when a backlight module is used in an LCD panel, the illumination uniformity of the outputting light applied to the LCD panel is usually one of the important factors that affect the overall performance of the LCD panel. Along with the expansion in the size of the LCD panels, the designs of the direct-light type backlight modules have become an area highly focused by the industry. Furthermore, providing uniform light illumination using a plurality of lamps, wherein the lamps are disposed in parallel with one another and distributed transversely with a selected interval, while preventing the formations of partial bright spots or partial dark areas has become one essential goal to achieve in the designs of the LCD panels.
FIG. 1 shows a conventional design of the backlight module disposed with a plurality of optical units for diffusing light and enhancing the illumination of the LCD panel. As shown in FIG. 1, the backlight module 10 includes a reflector plate 15 and a plurality of lamps 13 that are disposed in parallel with one another and distributed transversely with a selected interval. Furthermore, a plurality of optical units are disposed above the lamps 13, wherein the optical units are disposed in the following order: a diffuser plate 37, a bottom diffusion sheet 35, a brightness enhancement film 31, then a top diffusion sheet or dual brightness enhancement film 33. The light emitted from the lamps 13 will undergo a series of luminance and uniformity enhancing processes from traveling through the diffuser plate 37, the bottom diffusion sheet 35, the brightness enhancement film 31, and finally through the top diffusion sheet or dual brightness enhancement film 33. Thereafter, the light will enter a liquid crystal display (LCD) panel 50, which is disposed above the top diffusion sheet or dual brightness enhancement film 33.
From the practice of this conventional design, it can be concluded that as the transmittance of the diffuser plate 37, the bottom diffusion sheet 35, and the top diffusion sheet 33 decrease, the resulting performance on the light diffusion will be improved. However, when their transmittance decrease, the luminous efficiency of the LCD device will decrease correspondingly. As a result, a higher output power must be provided for increasing the brightness of the lamps 13. However, this may create a high power consumption problem. Furthermore, in order to improve the performance of light diffusion, a plurality of microstructures of the same pattern can be disposed on the bottom diffusion sheet 35. Each microstructure has the ability to alter the direction of the light traveling through it; therefore, light will scatter after traveling through the microstructures on the bottom diffusion sheet 35. However, since the directions of the light entering the bottom diffusion sheet 35 are different, using the microstructures of the same pattern can not improve the performance of light diffusion effectively.